The Great Erasure: Uncovering Earth’s Battered Past

Introduction

If you look at the Moon through a pair of binoculars, you see a surface scarred by thousands of impact craters. If you look at Earth from space, you see oceans, continents, and clouds—but almost no craters. Yet, Earth and the Moon formed together 4.6 billion years ago and have traveled through the same “shooting gallery” of space debris.

Where did Earth’s history go? In this investigation, you will use the Cratering & Surface Age Explorer to reconstruct the early history of our planet and discover how Earth “erases” its own past.

Part 1: Engage — The Mirror Image

Look at the two bodies in the simulation at 4.6 Billion Years Ago (BYA). Both appear relatively smooth.

1. Prediction: If both Earth and the Moon stay in space for the next 4 billion years, would you expect them to look the same or different today? Why?
2. “Need to Know” Questions: List two questions you have about why Earth looks so different from the Moon today.

Part 2: Explore — The Late Heavy Bombardment

Set the simulation to Play and observe the timeline from 4.6 BYA to 3.5 BYA. Ensure Weathering & Erosion, Plate Tectonics, and Volcanism are all ON.

1. Inquiry: Describe the rate of impacts during the first billion years (4.6 to 3.6 BYA) compared to the later years (1.0 BYA to Present).
2. Data Collection: Pause the simulation at 3.8 BYA and record the data below:

1. Observation: While the simulation is running, look at the Earth surface. What happens to a crater shortly after it is formed? Which specific process (Erosion, Tectonics, or Volcanism) seems to be the most “aggressive” at removing evidence?

Part 3: Explain — The Reset Button

Reset the simulation. This time, uncheck all three boxes (Weathering, Tectonics, Volcanism) for Earth. Run the simulation to the Present (0.00 BYA).

1. Comparison: How does the Earth’s surface look now compared to the Moon? What is the final “Oldest Surface Rock” age for Earth in this scenario?
2. Sensemaking: On the active Earth (with processes turned ON), the “Oldest Surface Rock” age eventually stops tracking the actual age of the planet (4.6 BYA) and stay much younger (around 3.8 BYA or less). Explain what this “age” actually represents in terms of radiometric dating. Is it the age of the planet, or the age of the last time the rock cooled/solidified?

Part 4: Elaborate & Evaluate — Constructing the Account

Using the evidence you gathered from the simulation, construct a scientific account of Earth’s formation and early history. Your account must address:

1. Bombardment History: Why do we use the Moon’s surface to infer what happened to Earth 4 billion years ago?
2. The Missing Evidence: Why is it so difficult to find rocks on Earth that are actually 4.6 billion years old?
3. Scientific Argument: A skeptic claims, “Earth was never hit by many asteroids because we don’t see the craters.” Use the concepts of Stability and Change and the evidence of Geological Active Processes to refute this claim.

Teacher Note: This task aligns with HS-ESS1-6 by requiring students to use lunar evidence and radiometric age “resets” to explain the scarcity of ancient materials on Earth.